In a non-aqueous electrolyte secondary battery such as a lithium-ion battery, a coating agent may be included for a purpose of increasing the durability, etc. In such a battery, typically during the initial charging, the coating agent undergoes electrical decomposition (typically reductive decomposition). A stable coating is then formed on the surface of the negative electrode active material. This can inhibit decomposition of the non-aqueous electrolyte when the battery is in use and thereby increase the durability of the battery.
As a conventional technical literature related to this, Patent Document 1 can be cited. Patent Document 1 discloses the use of an oxalato complex as a coating agent.